1. Field of the Invention
This invention relates to an electric double-layer capacitor having high capacitance and more particularly, to a solid type or solid state electric double-layer capacitor using a gel-like solid as the electrolyte material.
2. Background Art
Electric double-layer capacitors utilizing an electric double-layer, which are small-size high capacitance capacitors, are widely used as backup and auxiliary power supplies for personal computers, information communications equipment such as mobile phones, and electric appliances.
In terms of the type of electrolytic solution, the electric double-layer capacitors currently used in practice are generally classified into an aqueous solution system and a an organic solvent system. Of these, electrolytic solutions of propylene carbonate are generally used as a component of the organic solvent system. One typical capacitor is a coin-shaped cell in which the electrodes utilize activated carbon, activated carbon fibers or the like.
Such coin-shaped capacitors are liable to leakage of the electrolytic solution because of their structure, and suffer from the problem that the electrolytic solution leaked causes the corrosion of capacitor electrodes and internal equipment.
As a performance problem, the coin-shaped capacitors also suffer from self-discharge.
JP-A 302472/1994 discloses an electric double-layer capacitor using a gel-like solid polymer electrolyte. It is disclosed that poly(methyl methacrylate) (PMMA), poly(ethylene oxide), poly(propylene oxide), and poly(vinylidene fluoride) (PVDF) are used as the gel polymeric matrix. However, only PMMA is used in Examples while their capacitance is low. Examples using PVDF are disclosed nowhere. There is no description indicating what type of PVDF is useful or whether PVDF provides a capacitance comparable to PMMA.
JP-A 275469/1994 and Electrochimica Acta, vol. 40, Nos. 13-14, 2217-2222, M. Ishikawa, M. Ihara, M. Morita, Y. Matsuda disclose a capacitor comprising an electrolyte in the form of a gel using polyacrylonitrile (PAN) or poly(ethylene oxide)-grafted poly(methyl methacrylate) (PEO-PMMA) as a polymeric matrix. This capacitor, however, has a capacitance which is about 1/4 to about 1/5 of the capacitance of organic solvent electrolyte systems.